The roof sheathing is normally visible from the attic area. The sheathing is the material used over the rafters but under the roofing finished material. The most common type of sheathing used is plywood. It adds structural strength to the building and if kept dry has a very long life expectancy. Plywood and other laminated woods can sustain substantial damage if roof leaks are not repaired or poor venting causes condensation. Older homes and homes with exotic heavy roofs may be sheathed with wood planks. This type of sheathing is expensive but extremely durable. It is less prone to water damage because the boards used are whole pieces rather than glued or laminated and because they are smaller they allow air movement more easily, which helps prevent condensation damage. The inspector will be looking carefully for signs of roof leaks and condensation damage, which can be costly to repair.